Partly a feature-length advertisement for Random House’s most famous erotic novel series, partly an unintentional satire about the dire state of affairs for older female actors in Hollywood, partly a bland romantic comedy that sticks to formula, Book Club’s eye-raising hook centres on a group of autumnal friends who read 50 Shades of Grey and find their libidinal juices suddenly brought to the boil. It’s like a producer read one of those 2011 articles about middle-aged housewives renovating their own personal Red Rooms, click his ‘treatment’ fingers and then the thing sat in production for seven years. The Christian Grey…